Effect of chemical potential of carbon on phase transformation and corrosion of JLF-1 steel in a static lithium

The corrosion and the phase transformation of RAFM (Reduced Activation Ferritic/Martensitic) steel, JLF-1(Fe-9Cr-2W-0.1C), in static lithium (Li) were investigated. The specimens were exposed to static Li at 600 °C for 250 h. The carbon potential in Li was controlled by the carbide formation on inner surface of the crucible, which was made of Mo and Nb. These materials were expected to form stable carbide, and worked as carbon trap in Li, which resulted in the decrease in the carbon potential of Li. The effect of low carbon potential on the corrosion and the phase transformation was characterized by comparison with the test performed in the crucible made of Fe-9Cr and SUS316L (18Cr-12Ni), which has no effect as carbon traps. The low carbon potential caused by Nb and Mo caused the dissolution of carbon from the surface of JLF-1 specimen to Li. The depth of the phase transformation observed after the test in Nb crucible was deeper than that tested in Mo crucible. This was because the stability of the Nb carbide was larger than that of Mo carbide causing larger driving force for the dissolution of carbides from the surface.     

聚变堆低活化马氏体钢的发展

介绍了国际聚变堆低活化结构材料发展概况及趋势,以及国内发展自己特有的低活化马氏体钢的必要性。介绍了聚变堆结构材料——低活化铁素体/马氏体钢发展的必要性及迫切性,以及目前国际上包括欧洲、日本、美国等在此方面研究的进展概况及发展趋势,最后提出了国内发展自己特有的低活化马氏体钢——CLAM钢的必要性,并对目前的研究进展情况做了介绍。     

430℃下2.98dpa中子辐照后CLAM钢的拉伸和冲击性能

利用高通量工程试验堆HFETR开展了CLAM钢430℃下2.98dpa的中子辐照实验,通过辐照前后拉伸和冲击性能测试与对比分析,研究了CLAM钢的中子辐照硬化和脆化效应。结果显示,CLAM钢辐照后室温测试的抗拉强度和屈服强度分别为710 MPa和615 MPa,较辐照前分别下降16 MPa和-0.5MPa,总延伸率减小1%,断面收缩率下降4%,保持良好的强度、塑性和韧性。冲击测试表明,CLAM钢辐照前后韧脆转变温度基本相同,上平台能量无明显变化,约为217J,未出现明显辐照脆化。CLAM钢的抗辐照性能略优于其他低活化铁素体/马氏体RAFM钢在类似辐照条件下的性能。     

聚变制氢堆高温液态包层热工水力学新概念研究

在深入分析聚变堆包层设计要求和目前技术发展水平的基础上,根据热化学工艺制氢需要高温热的要求,提出了一个基于技术相对成熟的低活化铁素体/马氏体钢作为主要结构材料、高压氦气与液态LiPb合金作为冷却剂、具有创新性“多层流道插件”结构方案以获得高温热能的包层热工水力学概念,建立了热工水力学模型,在利用有限元数值模拟程序进行模拟计算的基础上分析了这种新概念包层的可行性。     

中国低活化马氏体钢CLAM研究进展

低活化铁素体/马氏体钢(RAFM钢)被普遍认为是未来聚变示范堆和聚变动力堆的首选结构材料。国际上给予了高度重视,许多国家都在研发其特有的RAFM钢。中科院等离子体物理研究所在与国内外多家单位的合作下发展了中国低活化马氏体钢———CLAM。本文总结了CLAM钢研制发展的主要进展,包括其成分优化设计、冶炼加工制备工艺、物理性能、机械性能、辐照性能及与液态LiPb的相容性等测试与研究以及各种焊接工艺研究等,并对今后的发展方向进行了展望。     

An Analysis of Ripple and Error Fields Induced by a Blanket in the CFETR

The Chinese Fusion Engineering Tokamak Reactor(CFETR) is an important intermediate device between ITER and DEMO. The Water Cooled Ceramic Breeder(WCCB)blanket whose structural material is mainly made of Reduced Activation Ferritic/Martensitic(RAFM) steel, is one of the candidate conceptual blanket design. An analysis of ripple and error field induced by RAFM steel in WCCB is evaluated with the method of static magnetic analysis in the ANSYS code. Significant additional magnetic field is produced by blanket and it leads to an increased ripple field. Maximum ripple along the separatrix line reaches 0.53% which is higher than 0.5% of the acceptable design value. Simultaneously, one blanket module is taken out for heating purpose and the resulting error field is calculated to be seriously against the requirement.     

Overview of Helium Cooled Ceramic Reflector Test Blanket Module development in Korea

Korea plans to install and test Helium Cooled Ceramic Reflector (HCCR) Test Blanket Module (TBM) in the ITER, because the HCCR blanket concept is one of options of the DEMO blanket. Currently, many design and R&D activities have been performed to develop the Korean HCCR TBM. An integrated design tool for a fusion breeder blanket has been developed based on nuclear technologies including a safety analysis for obtaining a license for testing in the ITER. A half-scale sub-module mockup of the first wall with the manifold was fabricated, and the manufacturability and thermo-hydraulic performances were evaluated. High heat load and helium cooling test facilities have been constructed. Next, the recent status of TBM material development in Korea was introduced including Reduced Activation Ferritic Martensitic (RAFM) steel, lithium ceramic pebbles and silicon carbide (SiC) coated graphite pebbles. Several fabrication methods of RAFM steel, lithium ceramic pebbles, and silicon carbide coating on graphite pebbles were investigated. Recent design and R&D progress on these areas are introduced here.     

Diffusion bonding beryllium to Reduced Activation Ferritic Martensitic steel: Development of processes and techniques

Beryllium was successfully bonded to a Reduced Activation Ferritic Martensitic (RAFM) steel with a maximum strength of 150 MPa in tension and 168 MPa in shear. These strengths were achieved using Hot Isostatic Pressing (HIP), at temperatures between 700 °C and 750 °C for 2 h and under a pressure of 103 MPa. To obtain these strengths, 10 μm of titanium and 20 μm of copper were deposited on the beryllium substrate prior to HIP bonding. The copper film acted a bonding aid to the RAFM steel, while the titanium acted as a diffusion barrier between the copper and the beryllium, suppressing the formation of brittle intermetallics that are known to compromise mechanical performance. Slow cooling from the peak HIP temperature along with an imposed hold time at 450 °C further enhanced the final mechanical strength of the bond.     

Impact of Material Configuration Behind First Wall on Helium Formation in In-Vessel Components of Fusion Reactor

The results of neutron transport calculations of the He formation based on the JENDL gas-production cross section file are discussed for some metals and alloys, namely ²⁷A1, Ti, ⁵¹V, Cr, ⁵⁵Mn, Fe, Ni, Zr, Mo, austenitic stainless steel (Ti modified 316 SS: PCA), Ni-base alloy (Inconel 625), ferritic steel (Fe-11Cr-1Mo: HT-9), Ti-base alloy (Ti-6A1-4V) and V-base alloy (V-5Cr-5Ti). Impacts of the two shields having the steel-rich and the H₂O-rich compositions and the two blankets having the Li₂O/Be-base and the liquid Li/Be-base compositions on the He formation rate in the above-mentioned metals and alloys are discussed. The relation between the He formation rate and the fast neutron flux (14.1 MeV>E>0.1 MeV) is investigated. The decrease of He formation at any distance Δ from the first wall more than Δ_as, the distance where the shape of neutron spectrum reaches its asymptotic form, is modelled by the simple formula based on the exponential dependence, as those reported so far for the fast neutron flux and the displacement damage rate.     

Microstructure and its influence on mechanical properties of CLAM steel

The microstructure of China Low Activation Martensitic steel (CLAM) and its influence on mechanical properties were investigated. The tensile test showed that the strength of CLAM (HEAT 0603A) was higher than that of HEAT 0408B at room temperature, and the reverse results were obtained at elevated temperatures. The results indicated that the microstructure was composed of dispersived carbide particles and lath martensite with high dislocation density. The main precipitation phases were Cr-rich M₂₃C₆ carbides precipitated mainly along the lath boundaries and prior-austenite grain boundaries and Ta-rich MX particles precipitated mainly in the laths and lath boundaries. The finer lath was the main reason for the higher strength of HEAT 0603A compared with HEAT 0408B at room temperature; contrasted with the lower strength at high temperature. Heavier hot forging deformation degree was considered as the main possible reason for the decrease of martensite lath width in HEAT 0603A.     

Assessment of toughness in long term service CrMo low alloy steel by fracture toughness and small punch test

Small punch test (SPT) is a miniature sample test technique which can evaluate in-service material properties with an almost non-destructive method. In this paper, the 2.25Cr1Mo steel samples serviced for 10 years in hydrogenation reactor (with temper embrittlement), 1.25Cr0.5Mo supper-pressure vapor pipe serviced for 14 years at 520 °C and several other low alloy steels have been studied by J_IC fracture toughness and SPT. The linear relationship between the small punch (SP) equivalent fracture strain and the fracture toughness of J_IC was created. The correlations applied to the experimental data indicated advantages of using SPT for the determining fracture toughness of in-serviced low alloy steels. Additionally, size affects the fracture pattern. Small punch samples of small size show dimple fractures whereas large fracture toughness samples show quasi-cleavage fractures.     

Thermal–hydraulic and thermo-structural analysis of first wall for Indian DEMO blanket module

The first wall (FW) is one of the most important components of any fusion blanket design. India has developed two concepts of breeding blanket for the DEMO reactor: the first one is Lead–Lithium cooled Ceramic Breeder (LLCB), and the second one is Helium-Cooled Ceramic Breeder (HCCB) concept. Both the concept has the same kind of FW structure. Reduced Activation Ferritic Martensitic steel (RAFMS) used as the structural material and helium (He) gas is used to actively cool the FW structure. Beryllium (Be) layer of 2 mm is coated on the plasma side of the FW as the plasma facing material. Cooling channels running in radial–toroidal–radial direction in the RAFMS structure are designed to withstand the maximum He pressure of 8 MPa. Heat transfer coefficients (HTC) obtained form the correlations revealed that required cooling could be achieved by artificially roughened surface towards the plasma-side wall of He cooling channel which helps to keep the RAFMS temperatures below the allowable limit. A 1D analytical and 2D thermal–hydraulic simulation studies using ANSYS has been performed based on the heat load obtained from neutronics calculations to confirm the heat removal and structural integrity under various conditions including ITER transient events. The required helium flow through the cooling channels are evaluated and used to optimize the suitable header design. The detail design of FW thermal–hydraulics, thermo-structural analyses, and He flow distribution network will be presented in this paper.     

Innovative materials for Gen IV systems and transmutation facilities: The cross-cutting research project GETMAT

Important Generation IV criteria for advanced fuel cycles are both improved efficiency and economical competitiveness. To reach these goals and keep high safety standards a key item is the availability of suitable structural materials. Ferritic/Martensitic (F/M) and Oxide-Dispersion-Strengthened (ODS) steels are indicated as the most promising candidates to withstand temperature, stress and irradiation fields expected in the core and primary system of most of the new generation reactors. In this context, the “Generation IV and Transmutation Materials” (GETMAT) project, sponsored by the EC, will contribute to the characterisation of ODS and F/M steels. The experimental and phenomenological aspects are complemented by the development of physical models aimed at describing and possibly predicting materials performance in operation.     

Evolution of microstructure and second-phase particles in Zr–Sn–Nb–Fe alloy tube during Pilger processing

Evolution of microstructure and second-phase particles (SPPs) in Zr–Sn–Nb–Fe alloy tube were investigated during Pilger process using electron backscatter diffraction, secondary electron and transmission electron microscopy imaging techniques. Results show that the Pilger rolled tubes present heterogeneous structures with the C axes of less deformed grains mostly concentrated in the axial direction. During the Pilger rolling, the increase of deformation caused weakening of linear distribution of second-phase particles. The mean diameters of the precipitates are in the range of 70–100 nm in all specimens, and the growth mechanism of SPPs follows second-order kinetics. The grain growth is controlled by Zener pinning in the Pilger rolling–annealing specimens. Clusters containing the Zr(Nb,Fe)₂ and β_Nb precipitates formed in the Zr–1.0Sn–1.0Nb–0.12Fe alloy. Most of the particles located in grain boundaries are the Zr(Nb,Fe)₂ Laves phase with hexagonal structure, and stacking faults have been found in the Zr(Nb,Fe)₂ precipitates. The types, morphology and distribution of precipitates depend on the constituent and structural fluctuations of the nucleation area.     

The effects of silicon and titanium on void swelling and phase stability in 12Cr-15Ni austenitic alloys irradiated with 46 MeV nickel ions

The structure of 20% cold-worked 12 wt%Cr-15 wt%Ni austenitic alloys with Si and Ti contents in the ranges 0.14-1.42 and <0.02-0.27 wt%, respectively, has been investigated by TEM following irradiation with 46 MeV Ni⁶⁺ ions to 60 dpa at 525, 575 or 625° C in the Harwell VEC. Increasing the Si content progressively reduced the void concentrations and swelling to zero at all three temperatures and the addition of Ti further reduced the void concentration and swelling. The higher Si alloys were structurally unstable during irradiations at 525 and 575°C, when γ'(Ni₃Si) particles, M₂₃X₆ type precipitates and grains of a bcc phase were formed. Small amounts of the γ' and bcc phases were observed following irradiation at 625° C, the principal precipitates being of the M₂₃X₆ type. Voids were present in both austenite and bcc phases in the lower Si alloys and segregation of an unidentified fcc phase was observed around voids. It was concluded that all the void nucleation occurred in the austenite phase and that the bcc phase resulted from the partial transformation of the austenite to α'-martensite during cooling from the irradiation temperatures. This occurred as a consequence of the M_s(α') transformation temperature being raised to well above ambient owing to elemental depletions of the alloy matrices resulting from precipitation and segregation.     

Microstructure and oxidation properties of 16Cr–5Al–ODS steel prepared by sol–gel and spark plasma sintering methods

The 16Cr–5Al oxide dispersion strengthened (ODS) ferritic steel was fabricated by sol–gel method in combination with hydrogen reduction, mechanical alloying (MA) and spark plasma sintering (SPS) techniques. The phase characterization, microstructure and oxidation resistance of the 16Cr–5Al–ODS steel were investigated in comparison with the Al free 16Cr–ODS steel. X-ray diffraction (XRD) patterns showed that the Al free and Al added 16Cr–ODS steels exhibited typical ferritic characteristic structure. The microstructure analysis investigated by transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS) revealed that Y–Ti–O complexes with particle size of 10–30 nm were formed in the Al free matrix and Y–Al–O complexes with particle size of 20–100 nm were formed in the Al contained high-Cr ODS steel matrix. These complexes are homogeneously distributed in the matrices. The fabricated 16Cr–5Al–ODS steel exhibited superior oxidation resistance compared with the Al free 16Cr–ODS steel and the commercial 304 stainless steel owing to the formation of continuous and dense Al₂O₃ film on the surface.     

Potential application of Laser Solid Forming Technology for fabrication of breeding blanket

To solve the fabrication of breeding blanket with complex structure, LSF (Laser Solid Forming) as a novel technology is proposed. The fabrication process of U-shaped first wall (one of components in breeding blanket) by LSF was shown. To verify the feasibility of LSF being applied in fabrication of breeding blanket, experiments based on CLF-1 (one of Reduced Activation Ferritic/Martensitic (RAFM) steels) by LSF (which is assigned as LSFed CLF-1 in this paper) is performed. The preliminary results show that main chemical composition is almost not changed from forgings of CLF-1 to LSFed CLF-1. As-deposited LSFed CLF-1 has high tensile strength, anisotropy and low ductility. However LSFed CLF-1 after proper heat-treatment can achieve homogenized structure, fully martensite phase, better tensile strength (ultimate tensile strength is 848 MPa) and comparable ductility (elongation is 17.3%), which suggests the possibility that LSF can be applied in fabrication of breeding blanket.     

Microstructural evolution of the China Low Activation Martensitic (CLAM) steel irradiated by H and He ion beams

China Low Activation Martensitic (CLAM) steel was irradiated at room temperature with different doses of He⁺ and H⁺ ion beams. TEM indicated that the microstructure of unirradiated CLAM steel consisted of laths, grain boundaries, dislocations and carbides. Electron diffraction patterns revealed that the microstructure of carbides at grain boundaries was primarily dominated by M₂₃C₆ carbide. Vacancy clusters were induced into the matrix after irradiation. TEM-EDX of carbides and matrices of unirradiated and post-irradiated samples were performed to investigate the composition of carbides and the effect of irradiation on the composition of carbides. Carbides from unirradiated and irradiated specimens at grain boundaries were found to be enriched with Cr. For irradiated specimens, concentrations of Cr increased as the irradiation dose was increased. Cr enrichment could lead to precipitation of additional phase.     

Studies on A-TIG welding of Low Activation Ferritic/Martensitic (LAFM) steel

Low Activation Ferritic–Martensitic steels (LAFM) are chosen as the candidate material for structural components in fusion reactors. The structural components are generally fabricated by welding processes. Activated Tungsten Inert Gas (A-TIG) welding is an emerging process for welding of thicker components. In the present work, attempt was made to develop A-TIG welding technology for LAFM steel plates of 10 mm thick. Activated flux was developed for LAFM steel by carrying out various bead-on-plate TIG welds without flux and with flux. The optimum flux was identified as one which gave maximum depth of penetration at minimum heat input values. With the optimized flux composition, LAFM steel plate of 10 mm thickness was welded in square butt weld joint configuration using double side welding technique. Optical and Scanning Electron Microscopy was used for characterizing the microstructures. Microhardness measurements were made across the weld cross section for as welded and post weld heat treated samples. Tensile and impact toughness properties were determined. The mechanical properties values obtained in A-TIG weld joint were comparable to that obtained in weld joints of LAFM steel made by Electron beam welding process.     

双束强辐照对氧化物弥散强化铁素体型合金强化相稳定性影响

采用双束复合辐照装置,研究了He存在条件下,强辐照对长期时效后的ODS合金中强化相(Y2O3)的稳定性和辐照损伤特征的影响。实验结果表明:双束强辐照下,ODS合金中强化相不稳定,发生聚集长大并造成附近基体中Ti、Y浓度增高,导致空洞尺寸和空洞肿胀增加,并对这一结果从理论上进行解释。